In many industrial fields it is necessary to continuously process sheets or webs of material unwound from a roll. Typically, in the corrugated board sector, unwinders with a plurality of means for supporting and unwinding rolls of web material, typically flat paper, are commonly used to produce corrugated board boxes or other articles. A plurality of corrugated board webs is fed to single facers and to double facers for the production of multi-layer corrugated board.
The unwinder comprises a splicing device (hereinafter also splicer) that makes the splice, i.e., the connection of the trailing edge of an expiring web material from a first roll being processed to the leading edge of a second web material of a second roll standing by. By automatically or semi-automatically splicing the leading edge and trailing edge of the two web materials, it is possible to operate the unwinder, and consequently the line containing it, in a substantially continuous manner.
In some cases, such as typically in the field of corrugated board manufacturing, it is preferable for the trailing edge and the leading edge of the two web materials to be spliced in close proximity of their respective free ends, to prevent problems in the subsequent processing steps. This requires particular measures to be taken to provide the device that carries out splicing, and sets some limits to the way in which the rolls of web material can be supported and unwound.
Modern unwinders and splicing devices for these purposes are described, for example, in EP 1609749 and in US 2004/0084133, the content of which is incorporated herein by reference.
When there is sufficient space on the two sides of the processing line, the rolls of web material are inserted from one side of the processing line and the empty cores are removed from the opposite side of the processing line. This is not possible in some plant layouts, for example as there is insufficient space on both sides of the processing line. This typically occurs when there is an obstacle, such as a wall, another processing line, or other obstacles on one of the sides of the processing line. Therefore, unwinders with three positions, which allow insertion and removal of the rolls from the same side of the line, have been developed. Exemplary embodiments of unwinders and processing plants of this kind are described in U.S. Pat. No. 7,441,579 and in U.S. Pat. No. 4,919,353, as well as in the two publications cited above (EP 1609749 and US 2004/0084133 A1).
The use of unwinders with three stations of this kind has some drawbacks. For example, their overall dimensions are relevant and this has a negative impact on the total length of the processing line. Moreover, unwinders of this type are complex and costly.
Therefore, there is the need to provide an automatic or semi-automatic unwinding and splicing system of web materials coming sequentially from rolls being processed to feed a processing line in a continuous manner, which entirely or partially overcomes the drawbacks of the prior art.